The invention relates to a device according to the characterizing part of patent claim 1.
Such a device is already known from DE 35 17 101 C1. It is used for examination of the heart with the aim of establishing whether an acute blockage of a coronary vessel by a blood clot is to be feared. For this purpose, an iodine contrast medium is injected into an arm vein of the patient and the patient is irradiated line-by-line simultaneously with two linearly collimated X-ray beams, of which one has an energy E1 just below the iodine absorption edge of 33 keV and the other has an energy E2 just above the iodine absorption edge. The two X-ray beams are focussed on the heart of a patient and impinge behind it on a detector with two counting chambers arranged parallel to one another at a distance, the signals of which are converted via a charge-sensitive A/D converter into digital signals and transmitted to a computer, which then composes in each case an image of the energy E1 and an image of the energy E2 and subtracts the images from one another logarithmically. It displays the resulting image on a monitor.
DE 39 01 837 A1 discloses a radiation detector which is capable of measuring the local distribution of high beam intensities with a high accuracy, a wide dynamic range and high sensitivity in short recording times. Applications lie, for example, in medical diagnostics for instantaneous recording of rapidly moved parts (coronary vessels). Pulsed radiation sources are used for this, the signals of the individual quanta which belong to a beam pulse being totalled in a proportional chamber and these individual signals per radiation source pulse thus obtained either already representing the required intensity signal or being totalled up electronically per image point over a number of radiation source pulses. DE 39 01 837 A1 furthermore provides the construction of such a detector. However, the disadvantage of this detector is that, together with conventional amplifier and converter circuits, the required image resolution cannot be achieved.
The object of the invention is to improve the device of the abovementioned type to the extent that the resolution of the resulting image is better, so that coronary vessels in particular can be shown more clearly.
This object is achieved by a device with the features of patent claim 1.
It comprises a high-sensitivity amplifier and analogue-digital converter with very high dynamics, with which the high absorption differences in iodine-filled bodies can be shown in linear form. In this way it is possible to show all three coronary vessels in spite of overlapping by iodine-filled ventricles.
In this connection it is pointed out that imaging of the coronary vessels is so difficult because on the one hand the heart is permanently moving, and on the other hand the contrast medium enters both the ventricles and the coronary vessels.
To achieve the object described it was therefore necessary to discover for the electronic circuits used a suitable component in the form of a current- or charge-digital converter which has a dynamic range of at least 18 bits, in order to achieve a sufficiently good resolution in the form of differences in colour or contrast.